Depends on how long the tanks been empty.

I made a smoker for a customer, and I saw rust in the bottom of the tank, and I filled with water and made my cuts with a zip disc on a grinder.

JMHO.

 

Making sure there has been adequate ventilation you can trickle in nitrogen, eliminating any oxygen and using a grinder with cutting discs. Caution is the name of the game.


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I have only recycled them, which entailed riddling them with bullet holes so the scrap yard would take them.

If its going to be a smoker, fire pit or something like that I would pull the valve stem and burn it, removing all the residual oil and what not from the inside.

 

I've been cutting numerous propane tanks lately. I use both plasma and a cutting torch. As soon as I remove the valve stem, I fill up the tank with water all the way up until it overflows. Then drain it and repeat this step three more times. Propane is heavier than air, but lighter than water. The tank will retain the strong odor, but I've managed to get all the gas out. Then I torch away to cut 'er open. No problems and I've drained, torched maybe two dozen or more now.

Recently, I made a thread here about a valve removal tool I made for those standard 5 and 20 gallon tanks. Here is the link. You can see some pics of the latest project too.

http://weldingweb.com/showthread.ph...-Home-made-propane-tank-valve-removal-tool&highlight=Propane+valve+removal+tool

One last thing, there should never be "oil" inside of a dedicated "propane tank."

 

It's not quite as dangerous as gas tanks, the tanks are meant to vent under fire. The least safe, but by far the most fun, is to open an inlet and outlet and throw a flare near it. If you get it perfect, you will get 15 seconds of a jet flame. If you are ready with a video camera, put a saddle on it.
The propane co near me cuts them all the time because that's the only way recyclers will take them. They just wash them out and go for it. I'm sure there are plenty of horror stories that will shut me down! They have a very smelly oil in them which is also somewhat flammable .

 

The tank will retain the strong odor, but I've managed to get all the gas out.

 

The tank will retain the strong odor, but I've managed to get all the gas out.

Vent the tank inverted so the gas settles out. Neutralized the methyl mercaptan odorant with bleach. Large thanks will have an oil residue which is likely compressor oil and methyl mercaptan. Get it on yourself and it will be adsorbed through the skin and you'll feel loopy and possibly slur your speech. Neutralize or pay the price... not only will it attack your nervous system but it will also ruin your shoes, clothes, and likely your marriage. I got some on my pants once... they hung on the clothes line for a year. The weather bleached them white... and I could still smell the odorant.

On a small BBQ cylinder if you add a little bleach to your rinse water you'll drive out the gas and neutralize at the same time. On large tanks you'll use a gallon diluted in 5 or 10 gallons of water and then roll the tank several times to ensure a good coating and neutralization.

On big tanks we normally leave vented inverted a couple days and dry with a few psi of compressed air. The gas is heavier than air so provided your tank is level it will be gas free soon enough.

 

I hook mine up to the car exhaust and take out one of the plugs in the tank. Run that a few minutes and do blackbarts test. Let the carbon monoxide take all the risk out of it.

 

Have to disagree with you - car exhaust is not a controlled method of getting the vapors out.
Heck, carbon monoxide is also flammable in the right concentrations.

Water filling is more controlled.

Throwing flares at a tank that you have now partially vented (meaning it could now have oxygen mixed with the propane) is asking for a boom, not a flame.

 

What is the bottled gas most commonly used to purge the tank? I'm in the early stages of oldtimers. and I have CRS.

 

Again, the most common way to purge is with liquid (H20) and not another gas. Why not go the simple, cheap, safe and effective way if flushing out completely with water? Has purging is a total waste of money.

 

I guess I shouldn't say they won't blow. I have just seen hundreds in wildfires vent,which looks like an explosion to most people. They will shoot flames 30' or so until they are burn't out. I do think simply washing them out with detergent and water should be enough.

 

So do you empty the water before you start cutting?

 

I just did two as a matter of fact. Took both valves off, flushed each with water twice, emptied the water, and cut the top off one and the bottom off the other using a jig saw/metal blade, then welded the two big pieces back together for one large tank. The smell will be there but there shouldn't be any gas. I was attempting to make a large oil drainage tank.

 

I've been wanting to ask the same question. Not to hi-jack but my mom just had her tank (500 gallon)replaced because the date tag is missing and the lp company will not fill it any more. She wants me to ct off each end to make hanging fire pits. I once cut up a 250 gallon diesel tank with a torch. I took it to the car wash and spent several dollars washing it out. I took all plugs out and let it dry and then stuffed it full of news paper and wove a wick and lit it. The first try it blew the news paper out of the opening and the second time it burned up inside the tank. I no longer have the nerve to do this. How thick will the ends of an older 500 gal LP tank be?

 

I've cut a bunch anywhere from 100 to 1000 gallons. ALWAYS fill with water! I fill it by screwing a hose connection in and let the water run while cutting with the torch. Makes for a nasty cut but you can clean the cuts up after. Once the cut is about half way around you can cut the water off and it's ok. Be sure to have the water take up all the space ( no air pockets ). I cut into an air pocket once on a thousand gal and almost chit my britches!!

 

Forgot to mention let the water run out of another hole, don't seal it up tight.

 

Again, use water or an inert gas such as CO2 or Nitrogen, both will completely eliminate any oxygen inside the tank and you only have to trickle them in. Still be very careful regardless of your method.


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I'm tell'n ya, water flushed in a propane tank is good enough. The gas is gone once water has pushed it completely out by overflowing. It's not that scary.

 

Papasmirf it was CO2 I couldn't think of last post. Never valued my life that much so...... I always piped in car exhaust let it vent out one of the nipples I took a valve out of for a few minutes.

 

Few years ago, 1st time I ever attempted it, I dumped in about half a box of baking soda then poured in about a pint of vinegar. After foaming stopped, I put a piece of duct tape over the opening, probably overkill, but it worked, , , -c-

 

Leave the water in the tank. I cut a grill size bottle that was full of water for a week, dumped it out, cut into it and it shot off my work table!

 

You could use nitrogen. All you need it to trickle it in and it will dissipate the oxygen. Please be very carefull of any container like that


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